The Big Bang: Does the concept make sense?

Thought for the day: Big Bangers claim that the universe's expansion rate is slowing down due to the gravitational attraction of all the different galaxies. One day, they claim, it will go in the opposite direction as gravitational forces overcome momentum, eventually bringing everything together in the Big Crunch. Which necessitates the question: Why, in the speculative idealism of Big-Bangology, would the universe have exploded in the first place? Black holes (high centers of mass) draw things together. Even the entire universe, they say, will one day collapse from its own extreme gravitation. Why, then, would it have done the opposite thing in the first place? I'm sure that they will have some explanation. Perhaps some new physical constant (like the "Cosmological Constant" proposed by Einstein which he later called "the biggest mistake of my entire career") will be created out of thin air to substantiate their theory. Or maybe they will say that in hypothetical hyper-space gravity has the opposite effect, pushing space apart while gravity draws mass itself together, and expansion/contraction happens when this gets out of balance. Since this is all speculation and not science, they can do whatever they want to keep their theory alive. This reminds me of a quote by Mark Twain (aka Samuel Clemens). To modify it a bit:

"The Big Bang Theory is like a frog. You can dissect the thing, but it has the disturbing tendency to die in the process."

Mainstream secular science would tend to agree. Let's keep the Big Bang together without looking at it too closely, and maybe it will fool some people. In Him, D3